Generate long numeric id of type String with auto increment

Question

I need to save entity with numeric id(15-25 digits) to H2 db. Since db doesn't support BigInteger (it's mapped to Decimal ), the only way to save such long numbers is String type.

Question: How I can generate such a numeric id of String type with auto increment?

UPDATE

ID should looks like: 123456789012345 (min 15 digits, max 25 digits)

Answer 1

You can still use a BigInteger behind the scenes.

Something like this should work for any number of digits and is thread safe.

private static final AtomicReference<BigInteger> id = new AtomicReference<>(BigInteger.ZERO);

public String nextId() {
    BigInteger next = id.accumulateAndGet(BigInteger.ONE, (x, y) -> x.add(y));
    return next.toString();
}

public void test(String[] args) {
    for ( int i = 0; i < 100; i++ ) {
        System.out.println(nextId());
    }
}

If your limits (15 - 25 digits) is hard then something like this would probably do.

private static final int MIN_DIGITS = 2;
private static final int MAX_DIGITS = 3;
private static final BigInteger start = BigInteger.TEN.pow(MIN_DIGITS-1);
private static final BigInteger limit = BigInteger.TEN.pow(MAX_DIGITS).subtract(BigInteger.ONE);

private static final AtomicReference<BigInteger> id = new AtomicReference<>(start);

public String nextId() {
    BigInteger next = id.accumulateAndGet(BigInteger.ONE, (x, y) -> {
        if(x.compareTo(limit) >= 0) {
            // Back to start.
            return start;
        }
        return x.add(y);
    });
    return next.toString();
}

public void test(String[] args) {
    for ( int i = 0; i < 1000; i++ ) {
        System.out.println(nextId());
    }
}

Note that for testing I have set the limits to 2 and 3 . You can adjust to your taste.

Answer 2

使用IDENTITY（START 10000000000），java Long，自动递增： http : //www.h2database.com/html/datatypes.html#identity_type